1. Field of the Invention
The present invention relates to vapor-compression refrigeration systems which are adapted to cool a fluid for domestic or other uses. More particularly the present invention relates to the vapor compression refrigeration system with two compressors, the second compressor receiving flashed gaseous refrigerant from a low temperature flash economizer and recompressing that gaseous refrigerant so that it may be recondensed in a high temperature flash economizer for use within the refrigeration system.
2. Description of the Prior Art
Refrigeration systems of the vapor compression type typically employ a compressor to increase a temperature and pressure of the gaseous refrigerant. Connected thereto is a condenser wherein gaseous refrigerant is cooled so that it changes state to a liquid refrigerant. Thereafter the refrigerant may be subcooled in a flash economizer wherein part of the refrigerant is vaporized absorbing heat from the remaining liquid refrigerant. The vaporized refrigerant has been typically drawn into the compressor for recycling through the condenser and the liquid refrigerant which has now been cooled is conducted to the evaporator or chiller. In the chiller, the refrigerant is evaporated absorbing heat from the fluid to be cooled, the now gaseous refrigerant being drawn into the compressor to complete the cycle. In the above described refrigeration system, the compressor is a multistage compressor such that the flashed refrigerant from the flashed economizer may be drawn into the compressor between stages allowing the flash economizer to be at an intermediate pressure to the condenser and the chiller. The basic patent dealing with a flash economizer was issued to Jones in 1942 and is entitled "Refrigeration", U.S. Pat. No. 2,277,647. Therein the flash economizer was located between the condenser and the evaporator and the flashed gaseous refrigerant therefrom was drawn into the compressor between the first and second stages and the liquid refrigerant which has been cooled in the flashing process is allowed to travel to the evaporator.
Other types of multi-stage compressors have been used with various economizers. In Wallard, et al, 3,232,074, entitled "Cooling Means for a Dynamoelectric Machine", there is disclosed an evaporator and a condenser wherein the flash economizer is located therebetween, the flashed gas being drawn into the second stage of a two stage compressor and the liquid refrigerant passing through the condenser and to the machine for cooling of the electric motor. Other typical economizers are shown in Ware, U.S. Pat. No. 3,165,905; in Osborne, U.S. Pat. No. 3,553,974; in Hieatt, et al, U.S. Pat. No. 2,684,579; and in Anderson, et al, U.S. Pat. No. 3,665,724.
In Jeket, U.S. Pat. No. 3,226,940 an economizer is used with a centrifugal compressor having a combination impeller blade such that flashed gas from the economizer may enter the centrifugal compressor in the middle of the blade thereby creating within a single compressor two separate pressure levels. In Granryd, U.S. Pat. No. 4,014,182 a method and apparatus are disclosed wherein an economizer is utilized with a single stage compressor such that liquid refrigerant is allowed to flow from the condenser to the economizer wherein gaseous refrigerant is withdrawn into the compressor until such time as the economizer temperature reaches the desired level. At such time a valve opens allowing the refrigerant to be drawn into the chiller from which the compressor removes the flashed refrigerant gas. The compressor runs continuously however, the suction line to the compressor is cycled alternately between the economizer and the condenser such that the compressor is always withdrawing refrigerant from either the economizer or the condenser and such that the refrigerant passing from the economizer to the condenser is always at the desired temperature.
In order to use a flash economizer within an existing vapor compression system having a single stage compressor it is necessary that a second compressor be provided such that the flashed gas can be compressed. Thereafter by providing an economizer-condenser this recompressed flashed gas may be condensed to a liquid and may be reflashed to further cool itself and the liquid from the initial flash process. This system is particularly applicable to refrigerants such as R-11 which are not adaptable to sensible heat subcooling. Latent heat cooling by means of a change of state is the only practical method to subcool R-11 and other similar refrigerants.
Prior refrigeration systems utilizing a flash economizer have required a multiple stage compressor to provide varying pressure levels for the flashing to occur. Refrigeration systems of a single stage compressor have previously not been adaptable for retrofit machinery to provide a flash economizing step since the pressure differential required has not been obtainable. The refrigeration system described hereafter is adaptable to be retrofitted to a single stage centrifugal compressor system so that a second compressor may be provided to recompress flashed gas from the low temperature flash economizer. The provision of an economizer-condenser which would condense the recompressed flashed gas aids in the overall efficiency of the system.
For similar refrigeration systems to the present invention see the following patent applications filed simultaneously herewith: Dual Flash Economizer Refrigeration System, Ser. No. 828,458; Thermal Economized Refrigeration System, Ser. No. 828,449; Thermal Economized Application for a Centrifugal Refrigeration Machine, Ser. No. 828,448; Supply Water Cooling for a Refrigeration System, Ser. No. 828,810; Flash Type Subcooler, Ser. No. 828,446;.